import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    static long sumOfGroup(int k) {
        // Return the sum of the elements of the k'th group.
        int start = 0;
        int sumComponent = 0;
        // Equation => k + 2(sum of sum of k (0,k-1) + k)
        
        for(int i = 0; i < k; i++)
            start++;
        
        for(int j = start; j < start + k; j++)
            sumComponent += j;
        
        return k + 2*sumComponent;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int k = in.nextInt();
        long answer = sumOfGroup(k);
        System.out.println(answer);
        in.close();
    }
}